Photosensitiers such as Rose bengal (RB), photofrin (PF) and benzoporphyrin monoacid ring (BPD) are used as photosensitizers in photodynamics therapy studies on cancer tumers utilizing multiphoton fluorescence microscopy (MPM). Although one-photon photophysical characterization of those photosensitizers are extensively investigated, the wavelength-dependence of two-photon excitation cross-section is not known. We have measured the absolute two-photon excitation cross-section (?(2)) of RB, PF, and BPD in the wavelength range of 810-980 nm using ~80 fs laser pulses at 82 MHz repetition rate. At each wavelength, power-dependent measurements were conducted to make sure that the detected fluorescence is due to two-photon absorption. From the wavelength-dependence of ?(2), a favorable excitation wavelength range (i.e. minimum photobleaching) for MPM imaging can be determined.